<!DOCTYPE html>
<html lang="zh-CN">

<head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>Document</title>
        <style>
                .red {
                        background-color: green;
                }

                .black {
                        background-color: black;

                }

                .blue {
                        background-color: blue;
                }

                .box {
                        width: 200px;
                        height: 90px;
                        font-size: 30px;
                }

        </style>
</head>

<body>
        <!-- 写在一个类里边，用空格隔开 -->
        <div class="black box "> 我靠</div>
        <div class="red box "> 我天</div>
        <div class="blue box ">卧槽 </div>

</body>

</html>